Raindrops of radius 1 mm and mass 4 mg are falling with a speed of 30 m/s on the head of a bald person.The drops splash on the head and come to rest. Assuming equivalently that the drops cover a distance equal to their radii on the head, estimate the force exerted by each drop on the head.

Explanation

Here, r = 1 mm = 0.001 m = `10^(-3)`m
m = 4 mg = `4 xx 10^(-6)` kg
s = `10^(-3)"m", v = 0, `u = 30 m/s
`therefore " " a = (v^(2) - u^(2))/(2s) = (-30 xx 30)/(2 xx 10^(-3)) m/s^(2)`
= -4.5 `xx 10^(5) m//s^(2)` (decelerating )
Taking the magnitude only, deceleration is `4.5 xx 10^(5) m//s^(2)`
`therefore` Force, F = 4 `xx 10^(-6) xx 4.5 xx 10^(5) = 1.8`N.